1. Field of the Invention
The present invention relates to a voltage regulating system for a vehicle alternator, particularly, a regulating system for providing powerful battery charging without causing the battery to be overcharged.
2. Description of the Related Art
JPA 4-275035 discloses a regulating system for a vehicle alternator, in which when the battery voltage becomes lower than a lower limit, a regulator reference voltage is set to a higher level to provide a powerful battery charging, and when the battery voltage becomes higher limit, the regulator reference voltage is returned to a normal level to provide a moderate battery charging. This publication also proposes a voltage regulation based on an average of the battery voltage in order to remove harmonic waves (i.e., ripple) of higher than 750 Hz contained in the current rectified by a full-wave rectifier of the alternator so that it can be compared with the reference voltage accurately.
In general, the battery voltage changes with charging condition of the battery such as an accumulated amount of charging or discharging current of the battery, and the battery charging current (i.e. the output current of the alternator) also changes as the engine rotating speed changes.
In the town driving where the engine speed changes repeatedly between idling speed and cruising speed, the engine speeds and the charging current (or the battery voltage) are generally low. Therefore, if the reference voltage is lowered every time in response to a temporary increase of the battery voltage, the battery is apt to be short of charging. However, if the normal reference voltage is set to be high to solve the above problem, the battery is apt to be over-charged when a vehicle runs at a high speed on a high way for a long time, thereby decomposing the battery electrolyte in a short time and deteriorating the battery
In the conventional voltage regulating system, the reference voltage is changed from one to another only according to the battery voltage irrespective of the vehicle running condition or conditions of the alternator. Therefore, the overcharging of battery can not be prevented sufficiently. Moreover, frequent change of the reference voltage causes frequent change of the engine load, which is not good for the engine control.